1. Field of the Invention
The present invention relates to a robot system, and more particularly to a technique for securing operator's safety in a robot system comprising a robot which is controlled by a robot controller, and at least one apparatus which is driven by a servomotor and carries out operation in cooperation with the robot.
2. Description of the Related Art
A robot controlled by a robot controller is driven by a servomotor, and the robot is used in a form of a robot system in which the robot is combined with another apparatus which carries out operation in cooperation with the robot in many cases. The number of apparatuses which cooperates with the robot is not limited to one, and a plurality of apparatuses are used in some cases.
In such a robot system, there exist an operation region such as a work stage which is driven by the servomotor, and a region (hereinafter referred to as “off-limits region”) where an operator is prohibited from entering for his or her own safety during the operation of the apparatus. Therefore, a technique for securing operator's safety is conventionally employed for an operator who approaches a dangerous apparatus or who enters the off-limits region.
FIG. 1 is a diagram for explaining the technique for securing safety which has conventionally been employed generally. In the example shown in FIG. 1, the robot system includes one robot, and apparatus-1 and apparatus-2 which are driven by servomotors, respectively. Power is supplied to the servomotors of the apparatus-1 and apparatus-2 by servo amplifiers provided in the apparatus-1 and apparatus-2, respectively. The robot is provided with a servo amplifier for a robot which supplies power to the servomotor. The operation of these servo amplifiers are controlled (including ON and OFF of power supply) by a robot controller.
Here, power to the servomotors of the apparatus-1 and the apparatus-2 are supplied through connection/interruption units provided in the apparatuses which are driven by the servomotors. The connection/interruption of power supply by each the connection/interruption unit is different from the connection/interruption control by means of the robot controller. The connection/interruption units are connected to the operator approach/entry detection units provided for the apparatus-1 and the apparatus-2, and when a notice that an operator approaches or enters is received from the approach/enter detection unit, the power supply to the servomotor is immediately interrupted.
As a unit for interrupting the power, a unit shown in FIG. 2 has already been established. As shown in FIG. 2, an essential portion of this unit comprises relays (their contacts are indicated as KA1, KA2, KA3) called safety relays or forcibly guiding type relays, and contactors (their contacts are indicated as KM1, KM2). A reference symbol M represents a servomotor of the apparatus-1 or apparatus-2. The open and close state of each contact in the drawings indicates that no operator's invasion is detected and power supply to the servomotor is being interrupted.
When the servomotor is being operating in a state in which operator's entry is not detected, the contacts of the relays KA1 and KA2 are closed, and the contacts of the relay KA3 maintains the illustrated state. With this operation, the contactors KM1 and KM2 are energized, and contacts of the contactors KM1 and KM2 provided in the power supply circuit to the servomotor are closed.
Here, if operator's entry is detected, the contacts of the relays KA1 and KA2 are opened, and electricity to the contactors KM1 and KM2 is interrupted. As a result, power supply to the servomotor is interrupted, and operator's safety is secured.
As illustrated in the drawings, all of the contacts of the relays KA1 and KA2 and the contactors KM1 and KM2 are made duplex, and even if a single contact breaks down, safety is secure. That is, even if one of the relays KA1 and KA2 breaks down, the power supply-interrupting function is not lost. It is possible to detect a single one of the relays KA1 and KA2 using the relay KA3. It is also possible to detect failure of the relay KA3 as far as the relays KA1 and KA2 are in normal states.
The related art is described in Japanese Patent Application Laid-open No. 59-159498. In this publication, there is described a technique that a doorway for access to a machine such as a robot is provided with photoelectric switches doubly, these double photoelectric switches detect that an operator approaches the machine from the doorway, and in accordance with the detection, the machine is automatically stopped.
In this conventional technique, a circuit structure for reliably interrupting power as described above is required. More specifically, the circuit in which a safety relay (forcibly guiding type relay) and a plurality of contactors are incorporated is required, as explained above. In this case, since special parts such as the safety relay are required, the number of parts is increased and thus, there is a problem concerning costs and reliability.